1. Field of the Invention
The present invention relates broadly to video signal processing. More particularly, it relates to technology for automatically detecting the position of the featuring part of a picture, such as an imageless part, in a television signal processing system.
2. Description of the Related Art
Conventional television receivers have screens which are endowed with an aspect ratio of 4:3. "High-vision" TV receivers, "wide" TV receivers, etc. whose screens are laterally longer owing to an aspect ratio of 16:9, are recently available as products. Such television receivers having the screen aspect ratio of 16:9 display laterally longer pictures as compared with the conventional television receivers having the screen aspect ratio of 4:3, and therefore bring forth the merit that the feeling of ambience is enhanced.
In a case where pictures based on video signals conforming to the ordinary aspect ratio of 4:3 are to be displayed by the television receivers having the screen aspect ratio of 16:9, various display examples are considered as stated below.
FIGS. 37A-37C and FIGS. 38A-38H are explanatory diagrams showing the examples in which the pictures based on the video signals conforming to the aspect ratio of 4:3 are displayed by the television receivers which have the screen aspect ratio of 16:9.
FIG. 37A illustrates the picture which is based on the video signal of the aspect ratio of 4:3. In case of displaying the full vertical direction of the picture as shown in FIG. 37B, imageless parts containing no image information appear on the right and left sides of the screen of the 16:9 TV receiver. On the other hand, in case of displaying the full lateral direction of the picture as shown in FIG. 37C (in case of enlarging the video signal and then displaying the enlarged video signal), several upper and lower lines of the 4:3 picture in the vertical direction thereof are missing.
Besides, FIGS. 38A, 38C and 38F illustrate the different pictures which are based on the video signals of the aspect ratio of 4:3, while FIGS. 38B, 38D, 38E, 38G and 38H illustrate the display examples, respectively. There are a large number of articles of movie (or motion picture) software in which the picture based on the video signal of the aspect ratio of 4:3 has imageless parts above and below an image part (containing image information) as shown in FIG. 38A, 38C or 38F. Especially the picture which contains characters at the lower part thereof as shown in FIG. 38F, is often found in the movie software.
By way of example, in a case where the picture based on the video signal of the aspect ratio of 4:3 is as shown in FIG. 38A, the image part can be displayed on the whole screen of the 16:9 TV receiver by setting an enlargement ratio of 1.5 as shown in FIG. 38B. However, in a case where the picture shown in FIG. 38A has changed-over to the picture having the imageless part of large area as shown in FIG. 38C or FIG. 38F, the enlargement ratio left intact incurs the situation of FIG. 38D where imageless parts are displayed at the upper and lower parts of the screen or the situation of FIG. 38G where the characters are partly lacked. Accordingly, the picture shown in FIG. 38C needs to be displayed by increasing the enlargement ratio as shown in FIG. 38E, and the picture shown in FIG. 38F by shifting its vertical position as shown in FIG. 38H.
It is very complicated, however, to set the enlargement ratio or the central position of the picture on each occasion for the purpose of attaining the optimum display for each of the various video signals as stated above. Therefore, if the enlargement ratio and the central position of the picture can be automatically set, the handling of the software based on the video signal of the aspect ratio of 4:3 becomes very convenient. The enlargement ratio and the central position of the picture may be determined from the detected values of the boundary positions between the image part and imageless parts of the picture in the vertical direction thereof, in other words, the No. of the start line of the image part of the picture (the start position of the image part in the vertical direction) and the No. of the end line of the image part (the end position of the image part in the vertical direction). Since, however, the video signal changes every moment, the correct boundary positions need to be detected every moment.
An example of prior-art apparatuses relevant to the above is a subtitles-region detection apparatus disclosed in the official gazette of Japanese Patent Application Laid-open No. 321387/1992 wherein only the part of the characters is extracted from the picture of the aspect ratio of 4:3 having the imageless parts at its upper and lower parts and containing the characters (i. e., subtitles) at its lower part as shown in FIG. 38F, and wherein the extracted part is inserted in another position of the picture so as to be displayed.
In the prior-art example, the end position of the image part as shown in FIG. 38F is detected, and the subtitles are moved by utilizing the detected position as the reference of the movement.
The arrangement of the essential portions of the prior-art example is illustrated in FIG. 39. The operation of detecting the image-part end position will be explained in conjunction with FIG. 38F. The prior-art apparatus comprises an input terminal 201, an integration circuit 202, a comparator 203, a counter 204 and an output terminal 205.
Referring to FIG. 39, a video signal is supplied to the input terminal 201. The integration circuit 202 computes and delivers the average level of each line of the video signal. The comparator 203 compares the output of the integration circuit 202 with a fixed value, and it delivers a low (`L`) level on condition that the former is smaller than the latter in the comparison. The counter 204 counts the number of successive lines affording the `L` level as the outputs of the comparator 203. On condition that the counted number has reached a predetermined value, the first one of the successive lines having afforded the `L` level is judged to indicate the image-part end position (as seen from FIG. 38F), which is delivered from the output terminal 205.
Meanwhile, in the field of television receivers, attempts have heretofore been made to better a video signal in points of luminance and tint in accordance with the content of a picture. A recent example is a method wherein the picture displayed on the screen of the TV receiver is divided into predetermined regions, and the picture qualities of the respective regions are adjusted independently of one another in accordance with the input video signal, thereby intending to attain a good picture quality at all times. Such a method of adjusting the picture quality of the television receiver is a technique disclosed in the official gazette of Japanese Patent Application Laid-open No. 154478/1991.
FIG. 40 is a block diagram showing a picture quality adjustment apparatus for the television receiver in the prior art. Referring to the figure, numeral 3001 designates an automatic picture-quality adjustment device, which subjects the video signal to the adjustment of the picture quality. An antenna 3002 receives video signals. A tuner 3003 selects a desired channel for reception, from among the received signals. A video intermediate-frequency (VIF) circuit 3004 detects the intermediate frequency of the selected video signal. In the adjustment device 3001, a level conversion circuit 3005 converts the level of the video signal. An analog-to-digital (A/D) converter 3006 converts the analog signal into a digital value. A microcomputer 3007 includes a level detector 3008 which detects the signal level on the basis of the digital signal, a controller 3009 regulates the gain of the level conversion circuit 3005 on the basis of the level detected by the level detector 3008, and a sampling signal generator 3010 which supplies a sampling signal to the A/D converter 3006. Numeral 3011 indicates a picture tube which images the video signal.
Next, the operation of the TV receiver shown in FIG. 40 will be explained. The video signal is supplied to the automatic picture-quality adjustment device 3001 through the antenna 3002, tuner 3003 and VIF circuit 3004.
The automatic picture-quality adjustment device 3001 subjects the supplied video signal to the picture quality adjustment involving brightness, contract, color densities, tint, etc., and supplies the adjusted video signal to the picture tube 3011.
Herein, the automatic picture-quality adjustment device 3001 operates as stated below.
The video signal delivered from the VIF circuit 3004 is sampled by the A/D converter 3006 in accordance with the sampling signal delivered from the sampling signal generator 3010, and the sampled data are supplied to the level detector 3008. Then, the level detector 3008 accepts the sampled data for, e.g., one frame and detects the signal level. The detected result for one frame is stored in a memory (not shown).
The controller 3009 sequentially reads out the data of the signal levels corresponding to the six domains A, B, C, D, E and F of a picture displayed on the screen of the picture tube 3011 as shown in FIG. 41, from among the data stored in the memory. Subsequently, it sets the conversion parameter of the level conversion circuit 3005 in order that each domain may be reproduced with the optimum picture quality conforming to the signal level. The conversion parameters of the six domains thus set are delivered as the control signals of the level conversion circuit 3005.
The level conversion circuit 3005 adjusts the picture qualities of the six domains A-F independently of one another in accordance with the conversion parameters supplied from the controller 3009, with respect to the input video signal supplied from the VIF circuit 3004. It supplies the signals of the adjusted picture qualities to the picture tube 3011.
Owing to the above operation, the picture qualities of the respective domains A-F displayed on the screen can be adjusted independently of one another.